1. Field of Invention
This invention relates to three-layer anti-reflection coatings for application to an optical system for substantially eliminating reflections over a relatively wide range of the visible spectrum.
2. Brief Description of the Prior Art
Three-layer anti-reflection coatings wherein the optical film thickness of the first and second layer is one-half of the designed wavelength while that of the third layer is one-fourth of the designed wavelength have been disclosed in U.S. Pat. No. 3,604,784 to Louderback, and granted on Sept. 14, 1971. A method of forming a film by mixing two kinds of metal oxides for obtaining a desired refractive index is also known.